1. Field of the Invention
The present invention relates to a braking control apparatus and method for vehicles and, more particularly, to the apparatus and method for controlling braking forces exerted respectively on the front wheels and on the rear wheels of an automobile.
2. Related Background Art
There are known braking controllers for controlling the braking forces distributed to the front wheels and to the rear wheels during braking. The technology disclosed in Japanese Patent Application Laid-Open No. 5-213169 is such a technique that when the deceleration reaches a predetermined value during braking, the hydraulic pressure to transmit the braking force to the rear wheels is maintained at the level at that time. The above application describes that this technique can prevent the rear wheels from locking prior to the front wheels and thus effectively prevent a sideslip of the vehicle during braking.
However, the braking force exerted on the rear wheels differs depending upon conditions of the vehicle even at fixed deceleration, and it is not always certain that the rear wheels lock. If the braking force is limited in spite of some margin of braking force left before locking of the rear wheels, the braking distance will become longer because of insufficient braking force.
In view of the above problem, an object of the present invention is to provide a braking control apparatus and method for vehicles satisfying both braking performance and stability of vehicle.
A braking control apparatus for vehicles according to the present invention comprises (1) vehicle speed determining means for determining a speed v of a vehicle, (2) deceleration determining means for determining a deceleration d of the vehicle, and (3) a braking control means for performing such control that when the deceleration d is not less than a predetermined value f(v) set according to the vehicle speed v so as to become smaller with increase in the vehicle speed, a braking force exerted on a rear wheel is limited as compared with a braking force exerted on a front wheel.
Further, a braking control method for vehicles according to the present invention comprises steps of (1) determining a speed v and a deceleration d of a vehicle, (2) determining if the deceleration d determined satisfies such a control condition that the deceleration d is not less than a predetermined value f(v) set according to the vehicle speed so as to become smaller with increase in the vehicle speed, and (3) performing such control that when said control condition is satisfied, a braking force exerted on a rear wheel is limited as compared with a braking force exerted on a front wheel.
In the apparatus and method according to the present invention, the braking force is controlled based on such control that the braking force exerted on the rear wheel is limited as compared with the braking force exerted on the front wheel when the deceleration is not less than the predetermined value according to the vehicle speed. The vehicle weight is shifted more toward the front wheel with increase in the deceleration. In the present invention, the braking force distributed to the front wheel is increased in the large deceleration region, thereby stabilizing the vehicle behavior. The predetermined value is set so as to become smaller with increase in the vehicle speed, whereby the braking-force control is carried out even at small decelerations in the high speed region where the vehicle tends to become instable, in order to keep the vehicle stable, and whereby the braking-force control is not carried out before the deceleration becomes relatively large, in the low speed region where the vehicle is relatively stable, in order to ensure the braking performance.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.